keel over vs topple

keel over

verb
  • To collapse in a faint; to black out, to swoon. 

  • To die. 

  • Of a vessel: to roll so far on its side that it cannot recover; to capsize or turn turtle. 

topple

verb
  • To totter and fall, or to lean as if about to do so. 

  • To overturn 

  • To overthrow something. 

  • To push or throw over 

How often have the words keel over and topple occurred in a corpus of books? (source: Google Ngram Viewer )